Zinc salt of mixed ester thiophosphates



Patented June 1, 1954 usirso FFlCE ZINC SALT OF MIXED ESTER THIOPHOSPHATES No Drawing.

Application March 29, 1951,

Serial No. 218,281

6 Claims.

This invention pertains to a new composition of matter prepared by reacting a mixture of two different alcohols with phosphorus pentasulfide (P285). In particular, this invention pertains to the zinc salts of a reaction product containing mixed diesters of dithiophosphoric acids pre pared by reacting phosphorus pentasulfide with a mixture or" two different alcohols (one alcohol containing not more than 4 carbon atoms, and the other alcohol containing from 6 to 18 carbon atoms).

ihe new compositions set forth herein are useful in additives in lubricating oil compositions; particularly useful in inhibiting oxidation of lubricating oil compositions. These new compounds are remarkably efiective in increasing the useful life of a lubricating oil composition which is susceptible to oxidation.

It is known that zinc salts of dialkyldithiophosphoric acids (wherein the alkyl groups are derived from the same alcohol) inhibit oxidation of lubricating oil compositions. It is also known that the alkyl groups of these zinc dialkyldithiophosphates may be or" high molecular weight or low molecular weight. Zinc dialkyldithiophosphates, wherein the alkyl groups are the same and each contain less thanil carbon atoms (e. g, 4 carbon atoms), are considerably less expensive than the zinc dialkyldithiophosphates containing alkyl groups which are the same and derived from higher molecular weight alcohols. In spite of this, these zinc dialkyldithiophosphates having alkyl groups derived from low molecular weight alcohols (e. g., alcohols of 4 carbon atoms) have not been widely marketed as lubricating oil additives. The main reason for this has been the insufiicient oil solubility of the zinc salts of low molecular weight dialkyldithiophosphoric acids to be able to prepare and market a concentrate in oil. This inability to ship concentrated oil solutions of these zinc salts due to the oil insolubility at normal storage conditions has more than offset the low cost of compounds per se. The same difiiculty of solubility pertains to the dialkyldithiophosphoric acids from which these zinc salts are derived.

It is'a primary object of this invention to prepare dialkyldithiophosphoric acids using two unlike low molecular weight alcohols as the source of the ester groups, and the zinc salts thereof.

It is another object of this invention to prepare zinc salts of: diesters of dithiophosphoric acids wherein the organo portions are derived from low molecular weight alchols, the dithicphosphates having sufficient oil solubility to prepare concentrated solutions of the zinc salts in oil of at least 35% at -20 F.

A further object of this invention is to prepare relatively low cost mixed diesters of dithiophosphoric acids.

These and further objects of the invention will be apparent from the ensuing description and the appended claims.

It has been discovered that the products obtained by the reaction of two different alcohols with phosphorus pentasulfide, and the zinc salts thereof, possess new and unique properties.

One of the alcohols used in the reaction contains less than 4 carbon atoms. These alcohols include methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, butyl alcohol, sec-butyl alcohol and tertiary outyl alcohol. For convenience, this group of alcohols will hereinafter be called the R1 alcohols.

The other alcohol used to form the reaction product of this invention contains from 6 to 18 carbon atoms. These include the following alcohols: hexyl, methylisobutylcarbin-ol, ethylisopropropylcarbinol, heptyl, iso-heptyl, Z-ethyl amyl, octyl, iso-octyl, 3-ethyl hexyl, Z-propyl amyl, decyl, undecyl, dodecyl, hexadecyl, octadecyl, etc. For convenience, this group of alcohols will hereinafter be known as the R 2 alcohols.

The R1 and R: alcohols need not be present in the reaction mixture in equal molar amounts. For certain types of oils and for certain purposes it may be preferred that the mole ratio of R1 aloe-- hols to R2 alcohols be from 1 to 5. It is particularly preferred to use a mole ratio of R1 alcohols to R2 alcohols from 2 to 4.

The reaction products of this invention are normally prepared by mixing two different alcohols, and causing the mixture of alcohols to react with phosphorus pentasulfide (PzSs) at temperatures ranging from about 120 15. to 200 F. For example, in the preparation or a reaction product of this invention, l moles of the desired alcohols (e. g., 3 moles of methyl alcohol and 1 mole of hexyl alcohol, wherein the mole ratio of methyl alcohol to hexyl alcohol is 3) are reacted with 1 mole of P285 for a time sufiicient to com-- plete the esteriiication. The zinc salts of the reaction mixtures are prepared by reacting the dialkyl dithiophosphoric acid preparation with Zinc oxide or zinc hydroxide at temperatures ranging from F. to 1'70 F.

The following examples illustrate methods of preparing the new compositions of this invention.

A mixture of 252 parts by weight (67 mole percent) of isopropyl alcohol and 206 parts by Weight (33 mole percent) of methyl isobutylcarbinol was placed in a glass reaction vessel. To this mixture was added 333 parts by weight of P2S5. The whole mixture was heated at 170 F. for 2 hours, after which the reaction mixture was cooled, and the product filtered to remove a small amount of unreacted P235.

In the preparation of the zinc salt, 650 grams of the acid intermediate thus obtained was added to 130 parts by weight of a petroleum oil having a viscosity of 300 SSU at 100 F. (used as a diluent), then 122 parts by weight of zinc oxide was gradually added at 130 F. The whole mixture was then agitated for 3 hours at 130 F., after which the water of neutralization was removed with calcium sulfate. The oil solution of the zinc salt had a pH of 6.? (after filtration), and contained 9.96% zinc, 9.43% phosphorus and 19.42% sulfur.

Example 2.--Reaction product of but'yl alcohol, methyiisobutylcarbinol and PzSs A mixture of 237 parts by Weight (7'? mole percent) or" sec-butyl alcohol and 98 parts by weight (23 mole percent) of methylisobutylcarbinol and 222 parts by weight or P285 was charged to a reaction vessel and agitated at 170 F. for a period of 2 hours. The reaction mixture was cooled and filtered to remove a small amount of unreacted P2S5. The resulting butyl methylisobutylcarbinol dithiophosphate was a dark red green liquid having a neutralization number of 193 (mgs. KOl-l/grarn), a viscosity of 35.7 SSU at 100 F., a specific gravity of 1.04 (60/60), and contained 24.0% sulfur and 11.9% phosphorus.

To the above mixture was added 87 parts by weight of zinc oxide, after which the whole was heated with agitation at 130 F. for 4 hours until a pH of 6.7 was reached. After the water of neutralization had been removed, the oil solution contained 7.6% zinc, 7.2% phosphorus and 15.0% sulfur.

The oil solubility of the zinc salts of this invention wherein the two different alcohols have certain mole ratios to each other is considerably greater than zinc salts having the same mole ratio of a mixture of two diester dithiophosphoric acids (wherein the ester groups in each acid are the same; that is, each acid contains only one of the ester radicals of the above mixed diester dithiophosphoric acid). For example, a 35% petroleum oil solution of a mixture of zinc di(secbutyl) dithiophosphate and zinc di- (methylisobutylcarbinol) dithiophosphate (mole ratio of 3.35) began to crystallize from solution within a period of 2 days at F. On the other hand, an 81% oil solution (same oil as above) of the zinc salt of the reaction product prepared according to Example 2 above was still clear after days at 20 F. Similarly, an 8% petroleum oil solution of a mixture of Zinc diisopropyl dithiophosphate and zinc di(methylisobutylcarbinol) dithiophcsphate (mole ratio of 2) began to crystallize from solution Within 3 days at +30 F. However, an 85% petroleum oil solution of the zinc salt prepared as in above Example 1 did not show any signs of crystallization after 34 days at +30 F.

The table below presents data concerning the effec 'veness oithe reaction products of this invention in reducing corrosion of metal parts due to oxidation of lubricating oils during the operation of internal combustion engines. To obtain these data, a stock Chevrolet engine was used. Instead of the normal babbitt bearings of -r in the Chevrolet engine, two of the connecting rods were modified to accommodate copper-lead bearing inserts, which were weighed before being assembled in the engine. The Chevrolet engine was operated at 3150 R. P. M., the engine jacket temperature was maintained at 300 F., the crankcase oil temperature was maintained at 280 F'., and the engine was operated for a period of 38 hours before being disassembled and the bearing inserts weighed. Before weighing, the bearing inserts were carefully washed with solvents to remove the oil therefrom.

Taole VBcgriig Test cig t oss Io. 01 SM?! (Mgs/Wholc I Bearing) 1 "I Rei'erence Oil for Test 17% 0. 2 b 558 2 Reference Oil 0.52% of the zinc salt of 36 Example 2 above.

3 Reference Oil for Test f ies. 4, 5 and 0 l, 102

4 i Reference Oil 0.81% zinc di(cctylph0nyi) clithiophospliatc.

5 Reference Oil 0.81% zinc di(cctylpi1cnyl) 344 ditliiophospliatc; i- 0.001% sulfurizcd alkylsubstituted calcium phenate.

0 Reference Oil i- 0.60% of the zinc salt 01' 76 Example 2 above; i- 0.091% sullurizcd alkyl-substitutcd calcium pheuate.

This reference oil was a California sovcnt-rciined parailinic base SAE 50 oil containing 0 0% weight a calcium allgyl sulfonate and 0.97% by \vei ht oi i ed aliryi-substitutcd calcium plienate Weight loss .irs.

v This reference oil 'is a Mid-Continent SAE 30 oil.

To illustrate still further the effectiveness of the reaction products of this invention as lubricating oil additives, a series of tests was run to determine the inhibition period of lubricating oils containing these reaction products. The inhibition period (the time in hours before grams of oil sample utilizes 1000 cubic centimeters of oxygen at 340 F.) of a medicinal white oii zero hours. When 0.19% of the zinc salt of above Example 2 was added to the medicinal white oil, the inhibition period was increased to 4.2 hours.

Other uses or the zinc salts of this invention include the use as anti-oxidants in greases, antiwear agents in silicate fluids, that is, organic esters or silicic acid, e. g., ortho silicate esters such as tetraethyl silicate, tetra(nhexy1) silicate, tetra(2ethyihexyl) silicate, etc.

The lubricating oils in which the new zinc salts of this invention may be incorporated include a wide variety of lubricating oils such as naplithenic base, parainn base, and mixed base mineral oils, other hydrocarbon lubricants, e. g., lubricating oils derived from coal products and synthetic oils, e. g., alkyiene polymers (such as polymers of propylene, butylene, etc, and mixtures thereof), alkylene oxide type polymers, dicarboxylic acid esters and liquid esters of acids of phosphorus. Synthetic oils of the alkylene oxice type polymer which may be used include those exemplified by allzylene oxide polymers (e. g., propylene oxide polymers) and derivatives, including alkylene oxide polymers prepared by polymerizing alkylene oxides (e. g., propylene oxide) in the presence of water or alcohols, e. g., ethyl aicohol, and esters of alkylene oxide type polymers, e. g., acetylated propylene oxide polymers prepared by acetylating the propylene oxide polymers containing hydroxyl groups.

I claim:

1. A zinc salt 0 mixed diesters of dithiophosphoric acids produced by reacting phosphorus pentasulfide with a blend of two different saturated aliphatic monohydric alcohols, one of said alcohols being a lower molecular weight alcohol and containing not more than 4 carbon atoms, the other of said alcohols being a higher molecular weight alcohol and containing from 6 to 18 carbon atoms, wherein the ratio of said lower molecular weight alcohol to said higher molecular weight alcohol has a value from 1.0 to 5.0.

2. The z nc salts of mixed diesters of dithiophosphoric acids produced by reacting phosphorus pentasulfide with a blend of two difierent saturated aliphatic monohydric alcohols at temperatures of 120 F. to 200 F., one of said alcohols being a lower molecular weight alcohol and containing not more than 4 carbon atoms, the other of said alcohols being a higher molecular weight alcohol and containing from 6 to 13 carbon atoms, the ratio of said lower molecular weight alcohol to said higher molecular weight alcohol having a value from 2 to 4.

3. The zinc salts of the mixture of esters of dithiophosphoric acids of claim 2, wherein one alcohol of the reaction blend is a butyl alcohol and the other alcohol of the reaction blend is a hexyl alcohol.

4. The zinc salts of the mixture of esters of dithiophosphoric acids of claim 2, wherein one alcohol of the reaction blend is a sec-butyl alcohol and the other alcohol of the reaction blend is a methylisobutylcarbinol.

5. The zinc salts of the mixture of esters of dithiophosphoric acids of claim 2, wherein one alcohol of the reaction blend is a propyl alcohol and the other alcohol of the reaction blend is a hexyl alcohol.

6. The zinc salts of the mixture of esters of dithiophosphoric acids of claim 2, wherein one alcohol of the reaction blend is an isopropyl alcohol and the other alcohol of the reaction blend is a methylisobutylcarbinol.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,939,951 Buchanan et al. Dec. 19, 1933 2,252,984 Rutherford et al. Aug. 19, 1941 2,261,047 Assefi et al. Oct. 28, 1941 2,368,000 Cook et al Jan. 23, 1945 

1. A ZINC SALT OF MIXED DIESTERS OF DITHIOPHOSPHORIC ACIDS PRODUCED BY REACTING PHOSPHORUS PENTASULFIDE WITH A BLEND OF TWO DIFFERENT SATURATED ALIPHATIC MONOHYDRIC ALCOHOLS, ONE OF SAID ALCOHOLS BEING A LOWER MOLECULAR WEIGHT ALCOHOL AND CONTAINING NOT MORE THAN 4 CARBON ATOMS, THE OTHER OF SAID ALCOHOLS BEING A HIGHER MOLECULAR WEIGHT ALCOHOL AND CONTAINING FROM 6 TO 18 CARBON ATOMS, WHEREIN THE RATIO OF SAID LOWER MOLECULAR WEIGHT ALCOHOL TO SAID HIGHER MOLECULAR WEIGHT ALCOHOL HAS A VALUE FROM 1.0 TO 5.0. 